CYTOCHEMICAL AND HISTOLOGICAL DETAILS OF MUSCLE-FIBERS IN THE SOUTHERN SMELT RETROPINNA-RETROPINNA (PISCES, GALAXIOIDEI)

Cytochemical and histological details are presented on the localizatio n of actomyosin adenosine triphosphatase (am-ATPase), succinic dehydro genase, lipid, and glycogen in the body musculature of the Southern sm elt Retropinna retropinna. The results clearly show that in addition t o the red and white muscle fibers a variety of pink fibers are present , which can be further classified according to fiber diameter, stainin g characteristics, and location. Using acid and alkaline preincubation with myofibrillar am-ATPase stain, both large and small diameter pink fibers were distinguishable from red as well as white fibers. It is s uggested that a transition between aerobic and anaerobic metabolisms e xists in intermediate zone fibers of which those with small diameters are likely to possess aerobic and those of large diameters a more anae robic capacity. The difference in metabolism could be related to fiber diameter and the associated constraints of large diffusion distances on oxygen availability.